Electronic paper has been developed based on a variety of display technologies, such as the electrophoretic display, the nanochromic display, the electrodeposition display, the liquid powder display, the twisting ball display or the liquid crystal display technology.
One of the ways to achieve multi-color states in electronic paper is the use of color filters. In general, color filters are placed on the front surface of a display panel and they generate different image colors depending on each sub-pixel's “on” or “off” state. For a reflective display, ambient light strikes on the display surface, a contrast is created through the difference between the reflected light of the “on” sub-pixels and that of the “off” sub-pixels which absorb the light. With color filters in front of a display panel, the light passes through the color filters before it hits the “on” and “off” sub-pixels and the reflected light passes back through the color filters. Since a color filter has limited transmittance, usually a significant loss in reflectance is observed when the light passes through the color filter twice, thus a significant reduction in the contrast and color saturation of the display. Therefore, although color filters have been used in the display industry, they have had rather limited success in the reflective type displays. In addition, the high cost associated with the color filters is another disadvantage.